1. Field of the Invention
The present invention relates to a plasma processing apparatus used for processing semiconductor wafers and the like by the action of a plasma generated by microwave.
2. Description of the Background Art
In recent years, semiconductor products have been increased in density and reduced in size to a great degree. Accordingly, some manufacturing processes of the semiconductor products employ a plasma processing apparatus for such processing as film deposition, etching and ashing. In particular, there is a tendency to use a microwave plasma apparatus since the microwave plasma apparatus can produce a plasma in a stable manner even in a high-vacuum state of a relatively low pressure, specifically from about 0.1 to several tens of mTorr, by using the microwave or a combination of the microwave and a magnetic field from a ring-shaped coil to produce a high-density plasma.
Such a plasma processing apparatus is disclosed for example in Japanese Patent Laying-Open Nos. 3-191073 and 5-343334 and Japanese Patent Laying-Open No. 9-181052 filed by the applicant of the present application. A general plasma processing apparatus using the microwave is described briefly below in conjunction with FIGS. 4 and 5. FIG. 4 shows a structure of a conventional and generally employed plasma processing apparatus and FIG. 5 is an enlarged view of a supporting portion for an insulating plate.
Referring to FIG. 4, this plasma processing apparatus 2 includes a process chamber 4 which can be evacuated, a mount base 6 with a semiconductor wafer W mounted thereon is provided in process chamber 4, and an insulating plate 8 is provided in an airtight manner to a ceiling portion opposite to mount base 6. Insulating plate 6 transmitting microwave is formed of aluminum nitride or the like in the shape of a disk, for example. Specifically, referring to FIG. 5, insulating plate 8 is attached in the airtight manner to a supporting shelf 12 via a sealing member 14 such as an O-ring. Supporting shelf 12 protrudes inward in the radial direction from a ring-shaped supporting frame member 10 made of aluminum for example that is provided on the upper end of process chamber 4.
On the upper side of insulating plate 8, there are provided a planar antenna member 16 in the shape of a disk with a thickness of several millimeters and a wave-delay member 18 formed of a dielectric for example for decreasing the wavelength of microwave in the radial direction of planar antenna member 16 as required. In addition, above wave-delay member 18, a ceiling cooling jacket 22 is provided that has a cooling channel 20 formed for flowing a cooling water therein in order to cool wave-delay member 18 and the like. Antenna member 16 includes a great number of microwave radiation holes 24 that are each an almost circular through hole or slit-shaped through hole. An internal cable 28 of a coaxial waveguide 26 is connected to the central part of planar antenna member 16 for guiding a microwave of 2.45 GHz for example produced by a microwave generator (not shown). The microwave is propagated radially in the radial direction of antenna member 16 and also discharged from microwave radiation holes 24 provided in antenna member 16 to be transmitted downward through insulating plate 8 into process chamber 4. The microwave produces a plasma in process chamber 4 for performing a predetermined plasma process such as etching and film deposition for semiconductor wafer W.
Most of the microwave radiated from planar antenna member 16 is supplied into process chamber 4 through insulating plate 8 below antenna member 16. On the other hand, a part of the microwave is propagated within insulating plate 8 in the radial direction thereof. This phenomenon is difficult to avoid.
Here, supporting frame member 10 holding the peripheral portion of insulating plate 8 is grounded and thus has a ground potential. Then, a standing wave 30 (shown diagrammatically in FIG. 5) is generated in insulating plate 8 in the radial direction thereof, the standing wave 30 having its node at the peripheral end of insulating plate 8. Consequently, in the region located slightly apart inward in the radial direction from the peripheral end of insulating plate 8, a high voltage is generated which locally causes an abnormal discharge 32 between the high-voltage region and supporting shelf 12. Abnormal discharge 32 causes the base aluminum which forms supporting shelf 12 to be cut off partially, and any metal other than aluminum that is contained in the base aluminum material could contaminate semiconductor wafer W or cause particle generation. In particular, abnormal discharge 32 described above occurs concentratedly at upper and lower corner portions P1 and P2 on the inner periphery of supporting shelf 12, since an electric field concentrates at angled portions such as upper right-angled corner portion P1 and lower obtuse-angled corner portion P2.
One object of the present invention is to provide a plasma processing apparatus capable of preventing an abnormal discharge from occurring between the insulating plate and the supporting frame member.
A plasma processing apparatus according to the present invention includes a process chamber having an internal space which can be evacuated and a ceiling with an opening, a supporting frame member placed along the periphery of the ceiling and including a ring-shaped supporting shelf protruding toward the center of the process chamber, an insulating plate having its peripheral portion supported by the supporting shelf of the supporting frame member and airtightly covering the opening of the ceiling of the process chamber, a mount base placed in the process chamber for mounting thereon a workpiece to be processed, a planar antenna member placed above the insulating plate and including a microwave radiation hole for transmitting therethrough microwave used for generating plasma, the microwave being transmitted through the insulating plate into the process chamber, and a gas supply unit for supplying a predetermined gas into the process chamber. The plasma processing apparatus of the invention is characterized in that the supporting shelf has an inner periphery including a corner portion shaped into a curve.
According to the present invention, the corner portion of the inner periphery of the supporting shelf which supports the insulating plate is curved. Field concentration at this corner is thus alleviated. Consequently, it is possible to prevent discharge from occurring concentratedly at this corner portion.
Preferably, the supporting shelf has the inner periphery including an upper-end corner portion and a lower-end corner portion, and at least one of the upper-end corner portion and the lower-end corner portion is shaped into a curve. More preferably, both of the upper-end corner portion and the lower-end corner portion are shaped into respective curves.
In order to effectively prevent field concentration at the corner portion, the corner portion of the inner periphery of the supporting shelf has a radius of curvature of at least 1 mm. The supporting shelf has a thickness of approximately 20 mm. Therefore, in consideration of this thickness, the corner portion of the inner periphery of the supporting shelf has a radius of curvature of at most 10 mm.
Preferably, the supporting shelf includes a supporting plane facing the insulating plate, and the supporting plane has a sealing groove in which a sealing member is held. For the purpose of avoiding field concentration at the sealing groove, a corner portion of the sealing groove that contacts the supporting plane is preferably shaped into a curve. According to one embodiment, the sealing groove has an inner corner portion and an outer corner portion that contact the supporting plane and the inner corner portion is shaped into a curve. The corner portion of the sealing groove is thus curved so that an abnormal discharge occurring at this corner portion can be avoided.
According to a preferred embodiment, an inner peripheral edge of the supporting shelf is located at a node of microwave propagated in the insulating plate in its radial direction. Then, there is substantially no potential difference between the corner of the inner peripheral edge of the supporting shelf and the insulating plate. Therefore, it is possible to enhance the effect of preventing occurrence of an abnormal discharge at this portion. In order to satisfy this positional relation, for example, the inner peripheral edge of the supporting shelf is apart inward from an outer peripheral edge of the insulating plate by a length equal to one half of wavelength of the microwave propagated in the insulating plate in the radial direction.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.